Groundwater Rise and Associated Flooding in Coastal Settlements Due To Sea‐Level Rise: A Review of Processes and Methods

• Published in: Earth's future Vol. 10; no. 7
• Main Authors: Bosserelle, Amandine L., Morgan, Leanne K., Hughes, Matthew W.
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.07.2022; Wiley
• Subjects: Aquifers; Climate change; Climate effects; Coastal environments; Coastal flooding; Coastal processes; Coastal zone; Coasts; Drainage; Earthquakes; Environmental monitoring; Evaluation; Flooding; Floods; Geology; Groundwater; Groundwater levels; Hydrogeology; Infrastructure; Interpolation; Rain; Regions; Saline water; Saline water intrusion; Salt water intrusion; Sanitation; Sea level rise; Shallow water; Surface water; Sustainable development; Tidal waves; Urban development; Urbanization; Water monitoring; Water quality; Water table
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2021EF002580

Coastal settlements are experiencing the effects of climate change‐induced sea‐level rise, including a significant but often poorly‐characterized impact on groundwater. The shallow water tables present in the built coastal environment contribute to an increased risk from natural hazards such as groundwater flooding and saltwater intrusion. Historical urban development was accompanied by impacts on shallow groundwater, and in the future subsurface environments, including underground infrastructure, will face additional pressure. This article reviews processes of the coastal groundwater zone and simulation tools used to evaluate possible impacts of sea‐level rise. The benefits and limitations of the two main methods to assess coastal groundwater rise and contribution to flooding are discussed using studies and investigations up to 2021. The review addresses challenges associated with the simulation tools to evaluate changes in urban hydrogeology due to sea‐level rise. The models reviewed do not specifically estimate groundwater contribution to land‐surface flooding. We highlight a critical need for methodology comparisons between spatial interpolation and numerical tools that will guide future work. An adequate validation of assessment methods is required and will be supported by improved coastal groundwater monitoring networks focused on water quality, saltwater intrusion, and continuous groundwater levels records. From current monitoring practices, evidence for groundwater rise with rising sea level is not widely observed at present. New monitoring sites are recommended near the coastline and tidally influenced surface water bodies, to better evaluate the rise of the water table and impacts on infrastructure. Plain Language Summary The presence of shallow groundwater beneath coastal settlements exposes these locations to a threat from below. Groundwater can contribute to surface flooding and a large part of the existing underground infrastructure is already under the water table, posing significant risks to old, deteriorating systems. When the sea level rises, groundwater rises and flooding risk increases. This exposes underground structures and networks, building foundations and low‐elevation roads to wetter conditions. Consequently, damage to coastal infrastructure can be expected from rising sea levels. In this article, we review the methods available to assess where the changes in groundwater conditions will occur, the current and future groundwater interactions with urban infrastructure, and the hazards associated with the occurrence of shallow groundwater. We discuss the tools available to simulate groundwater rise with sea‐level rise including benefits and limitations of those methods. We highlight that measurements of coastal groundwater quality to monitor seawater contamination are commonly documented but there is a lack of information on the impact of rising sea levels on groundwater levels. Within coastal cities and settlements along the shoreline, we recommend that water levels are recorded with new automatic monitoring networks specifically designed to evaluate the impacts of sea‐level rise on coastal groundwater and infrastructure. Key Points Groundwater rise with sea‐level rise already exposes coastal settlements to hazards such as groundwater flooding and saltwater intrusion Subsurface networks and underground infrastructure will likely be further exposed to damage from rising groundwater under sea‐level rise Tools for simulating flooding in coastal areas are expanding to integrated surface water, groundwater and underground infrastructure models